With your child's weekly piano lesson coming round (or violin or oboe or whatever), the inevitable debate rears its ugly head about "how often have you practised this week?". Sadly, classical music demands many hours of practice: even international stars seem to spend a terrifying proportion of their waking hours practising, regardless of how much native talent they have.
The answer to the question "how much practice do I need" depends largely on what standard you want to achieve. If you just want to learn a bit about the instrument and become competent to play a few pieces nicely, you'll get away with an hour or three a week. If you want to play in a band or orchestra without making a fool of yourself, you'll need more. But how much do you need to become a real expert, a world-class performer?